Asbestos

(endorsed 1996)

Guideline

Data are insufficient to determine a guideline value for asbestos in drinking water.

General description

Asbestos is a general term for certain fibrous silicate minerals. It can be present in drinking water from the dissolution of asbestos-containing minerals, industrial effluent, atmospheric deposition, and deterioration of asbestos cement pipes commonly used in water distribution systems.

The chemical and crystalline structure of asbestos results in products with a high tensile strength, durability, flexibility, and heat and chemical resistance. Asbestos has been used in construction materials such as asbestos cement pipes and sheets, electrical and thermal insulation, brake linings and clutch pads.

The extent of asbestos contamination of food has not been well studied because of the lack of a simple and reliable analytical method. Limited data indicate that the amount in food may be 10 times higher than that found in drinking water.

Studies in the United States and Canada have reported typical asbestos fibre numbers in drinking water of less than 1 MFL (million fibres per litre). Severe deterioration of asbestos cement pipes has been known to produce fibre numbers of up to 2000 MFL.

Typical values in Australian drinking water

Australian drinking water supplies have not been routinely monitored for asbestos; however, fibre numbers are probably similar to those reported overseas.

Treatment of drinking water

Asbestos fibre numbers can be reduced by the standard water treatment processes of coagulation and filtration.

Measurement

Asbestos can be analysed using transmission electron microscopy with identification of the fibres by selected-area electron diffraction. This procedure is both costly and time consuming and is not suitable for routine analysis. The limit of determination is about 0.3 MFL.

Health considerations

The health hazards associated with inhalation of asbestos have been recognised for a long time. They include asbestosis, cancer of the bronchial tubes, malignant mesothelioma, and possibly cancers of the gastrointestinal tract and larynx (IPCS 1986).

In contrast, there has been little evidence that ingested asbestos causes cancer. A number of quite extensive epidemiological studies have been carried out on the effects of asbestos in the water supply. On the basis of these data there is no demonstrated excess risk of cancer even with high numbers of asbestos fibres in drinking water.

It is not clear whether asbestos fibres ingested in drinking water can pass through the walls of the gastrointestinal tract in sufficient numbers to cause adverse effects. Experiments with laboratory animals indicate that penetration, if it occurs at all, is extremely limited.

Animal studies on the carcinogenic effects of ingested asbestos have been inconclusive.

Asbestos did not exhibit mutagenic activity in tests with bacteria but has induced chromosomal aberrations, malignant transformation of mammalian cells in vitro, and various biochemical alterations associated with tumour promoters.

The International Agency for Research on Cancer has concluded that asbestos is carcinogenic to humans by the inhalation route (Group 1, sufficient evidence of carcinogenicity in humans) (IARC 1987).

Derivation of guideline

There are insufficient data to set a guideline value for asbestos in drinking water. It is unlikely, however, that the numbers of asbestos fibres present in most drinking water supplies would be a health concern. The weight of evidence indicates that ingested asbestos is not hazardous to health.

The guideline should be reviewed as soon as more toxicological data are available.

References

IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.

IPCS (International Programme on Chemical Safety) (1986). Asbestos and other natural mineral fibres. Environmental Health Criteria, 53. World Health Organization, IPCS.